This invention relates to leak detection methods and systems, and more particularly, to automotive fuel leak detection in a vapor handling system.
In a vapor handling system for an automotive vehicle, fuel vapor that escapes from a fuel tank is stored in a canister. If there is a leak in the fuel tank, the canister, or any other component of the vapor handling system, fuel vapor could exit through the leak to escape into the atmosphere.
The present invention provides a method of leak detection in a closed vapor handling system of an automotive vehicle while an engine is running. This method includes providing a pressure sensing element that obtains at least one pressure signal, closing a control valve and a shut off valve to seal the system from the engine and an atmosphere, generating a vacuum by opening the control valve, analyzing the at least one pressure signal at threshold times, comparing the at least one pressure signal to at least one pressure control value, and determining a leak condition if the at least one pressure signal is not less than the at least one pressure control value.
The present invention also provides another method of leak detection in a closed vapor handling system of an automotive vehicle while an engine is running. The method includes providing differential tank pressure sensor that provides pressure, closing a canister purge control valve to seal the system from the engine and an atmosphere, waiting for a first period of time, closing a shut off valve, waiting for a second period of time, determining a pressure sensor offset, estimating a correction value for vapor generation, aborting the leak detection if the correction value is greater than a control correction value, calculating a pressure mean value, dropping the pressure to a first threshold pressure by opening the control valve for a third period of time, detecting a tank cap missing condition if a second threshold pressure is not reached within a third period of time, detecting a large leak condition if the pressure drops below the second threshold pressure and above the first threshold pressure within the third period of time, aborting the leak detection if the speed of the automotive vehicle is greater than zero, ending the leak detection if a fuel volume is not within a control volume range, evaluating a pressure slope over a fourth period of time, calculating a corrected pressure slope using the correction value for vapor generation, and determining a leak diameter by comparing the corrected pressure slope to pressure control values within threshold times.
The present invention also provides an automotive evaporative leak detection system. The system includes a pressure sensing element, a control valve, a shut off valve, a processor operatively coupled to the pressure sensing element and the shut off valve and receiving pressure signals from the pressure sensing element and sending signals to the control valve and the shut off valve. The processor closes the control valve and the shut off valve, generates a vacuum, depressurizes the system using the vacuum, controls the vacuum by opening the control valve, analyzes the pressure signal at threshold times, compares the pressure signal to pressure control values, and determines a leak condition.
The present invention further provides another automotive evaporative leak detection system. This system includes a differential tank pressure sensor located on a conduit between a fuel tank and a canister, the canister communicating with an engine and an atmosphere, the fuel tank communicating with the engine, a shut off valve located between the canister and the atmosphere, a control valve located between the canister and the engine, and a processor operatively coupled to the pressure sensing element and the shut off valve and receiving pressure signals from the pressure sensing element and sending signals to the control valve and the shut off valve. The processor closes the control valve, waits for a period of time, closes a shut off valve, determines a pressure sensor offset, estimates a correction value for vapor generation, calculates a pressure mean value, drops the pressure to a threshold pressure, detects a tank cap missing condition, detects a large leak condition, aborts the diagnosis, evaluates a pressure slope, calculates a corrected pressure slope, and determines a leak diameter by comparing the corrected pressure slope to pressure control values within threshold times.